1. Field of the Invention
The present invention relates to a recording material determination apparatus and to an image forming apparatus to which the recording material determination apparatus is applied. More particularly, the present invention relates to a recording material determination apparatus configured to determine the type of a recording material using a sensor that determines a surface condition of the recording material and a sensor that determines a grammage of the recording material, and to an image forming apparatus to which the recording material determination apparatus is applied.
2. Description of the Related Art
Generally, an image forming apparatus, such as a copying machine or laser printer, forms a toner image on a photosensitive drum, serving as an image carrier, using toner, serving as a developer, and transfers the formed toner image onto a recording material. Then, the image forming apparatus fixes the toner image transferred to the recording material by heating and pressing the toner image under predetermined conditions. The predetermined conditions include a temperature to be set according to the type of a recording material (e.g., a quality, a thickness, a grammage, and a surface condition of the recording material) and a speed of conveying the recording material. Thus, the quality of an image formed according to the type of the recording material is maintained. That is, in the case of forming an image on a recording material, the type of the recording material may be determined before forming (printing) the image on the recording material. By doing so, fixing conditions may be more precisely set according to the determined type of the recording material.
Conventionally, in an image forming apparatus, the type (e.g., gloss paper (glossy paper), cardboard, thin paper, plain paper, overhead transparency (OHT)) of the recording material is set by a user via an operation panel provided on the apparatus. The fixing conditions can be changed according to user settings.
Some recent image forming apparatuses incorporate a recording material determination sensor and have the function of automatically determining the type of a recording material supplied thereinto using the sensor, in addition to the function of determining the type of a recording material based on user settings. Additionally, the recent image forming apparatuses variably control the fixing conditions according to the type of the recording material, which is determined by the sensor. The conditions that are variably controlled according to the type of the recording material are not limited to the fixing conditions. Developing conditions for developing a toner image on the photosensitive drum and transfer conditions for transferring the toner image to the recording material can be variably controlled according to the type of the recording material.
Some image forming apparatuses automatically determine the type of a recording material by, e.g., capturing a surface image of the recording material using a charge-coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor and determining the surface condition of the recording material using the captured image data. Such image forming apparatuses determine the type of a recording material using a method of detecting the smoothness of a surface of the recording material according to the magnitude correlation among the densities of pixels represented by the captured image data. Japanese Patent Application Laid-Open No. 2005-128004 discusses another method of determining the thickness or grammage of a recording material according to an amount of light transmitted through the recording material.
However, particularly, in a case where the grammage of a recording material is determined, the determination accuracy in the conventional method may be insufficient. For example, according to a conventional method of determining the thickness of a recording material based on an amount of transmitted light, even when the thickness of the recording material has the same value, the transmitted light can vary depending upon the whiteness degree, the color, and the fiber density of the recording material. That is, according to the conventional method using the amount of transmitted light, the thickness of the recording material can be determined with a certain level of accuracy. However, it is difficult to finely determine the grammage of a recording material. Note that the “grammage” of a recording material is defined as a weight of a sheet of the recording material in the units of gram per square meters (g/m2).
Japanese Patent Application Laid-Open No. 2004-107030 discusses a method of determining the type of a recording material, such as paper, by detecting an ultrasonic wave reflected from the recording material, and a method of determining the thickness of a recording material by detecting an ultrasonic wave transmitted through the recording material.
Japanese Patent Application Laid-Open No. 2004-107030 discusses also an apparatus in which an ultrasonic transmitter is provided on one of sides of a recording material while an ultrasonic receiver is provided on the other side of the recording material. The ultrasonic transmitter irradiates an ultrasonic wave to the recording material to vibrate the recording material. The ultrasonic receiver receives an ultrasonic wave transmitted through the recording material due to the vibration of the recording material. Then, the thickness of the recording material is determined according to a signal corresponding to the received ultrasonic wave.
When the type of a recording material is determined, the type of the recording material can be determined in more detail by finally determining the type of the recording material using both a result of determining the thickness or grammage thereof and a result of determining the surface condition thereof.
Thus, it is considered that the type of a recording material can be determined by employing both the method discussed in Japanese Patent Application Laid-Open No. 2004-107030 to determine the thickness or grammage of the recording material and the method discussed in Japanese Patent Application Laid-Open No. -04 to determine the surface condition of the recording material.
However, in a case where detection operations are substantially simultaneously performed using both the methods, when an image of a surface of a recording material is captured by a CCD sensor or a CMOS sensor to determine the surface condition of the recording material, an image is captured in a state in which the recording material is vibrated with an ultrasonic wave. That is, the surface of the vibrated recording material is captured. Thus, there is a possibility that an unfocused image of the surface of the recording material is captured. In a case where a smoothness representing the surface condition of the recording material is detected according to the unfocused image of the surface of the recording material, the type of the recording material may be misdetermined.
In a case where the type of the recording material is misdetermined, e.g., where gloss paper (glossy paper) is misdetermined as plain paper, fixing conditions irrelevant to the correct type of the recording material are set. Accordingly, it is assumed that the picture quality of the image is degraded.
On the other hand, recently, more various types of recording materials are used by users. Accordingly, it is desired to more accurately determine the type of a recording material so as to appropriately set image forming conditions according to the type of the recording material.